# Reaction enthalpy at non-standard conditions

Hi

I am tutoring a pupil in high-school out of necessity (no other teachers avail), while I am not so acquainted anymore with chemistry. The pupil showed me a question concerning the calculation of the reaction enthalpy which looked somewhat as follows:

1. Problem statement, all variables and given/known data

Calculate the reaction-enthalpy for the reaction:

$C_3H_8 (g) + 5O_2 (g) \rightarrow 3CO_2 (g) + 4H_2O (g)$

at 30$^\mathrm{o}$C and 1.08 atm.
The formation enthalpies at standard conditions and the heat capacities at constant pressure were known.

2. Relevant equations

3. The attempt at a solution

NOTE: I am not sure anymore about the exact reaction or the exact temperature and pressure, the above is meant as a generic example of the exercise that the pupil showed me.

As I remember, first the formation enthalpies at the non-standard conditions should be computed. This should be done in two steps:

1) Take into account the increase in temperature assuming constant pressure: use $\Delta H = C_p\Delta T$.
2) Take into account the increase in pressure assuming constant temperature.

I cannot remember how the second step should be computed, neither did I find some appropriate formula during a quick search.
Is the current approach the correct one? Could it be possible to give me some more information about how to proceed?